US considered poisons for assassinations (Associated Press)WASHINGTON --In one of the longest-held secrets of the Cold War, the U.S. Army explored the potential for using radioactive poisons to assassinate "important individuals" such as military or civilian leaders, according to newly declassified documents obtained by The Associated Press.

Approved at the highest levels of the Army in 1948, the effort was a well-hidden part of the military's pursuit of a "new concept of warfare" using radioactive materials from atomic bombmaking to contaminate swaths of enemy land or to target military bases, factories or troop formations.

Military historians who have researched the broader radiological warfare program said in interviews that they had never before seen evidence that it included pursuit of an assassination weapon. Targeting public figures in such attacks is not unheard of; just last year an unknown assailant used a tiny amount of radioactive polonium-210 to kill Kremlin critic Alexander Litvinenko in London.

No targeted individuals are mentioned in references to the assassination weapon in the government documents declassified in response to a Freedom of Information Act request filed by the AP in 1995.

The decades-old records were released recently to the AP, heavily censored by the government to remove specifics about radiological warfare agents and other details. The censorship reflects concern that the potential for using radioactive poisons as a weapon is more than a historic footnote; it is believed to be sought by present-day terrorists bent on attacking U.S. targets.

The documents give no indication whether a radiological weapon for targeting high-ranking individuals was ever used or even developed by the United States. They leave unclear how far the Army project went. One memo from December 1948 outlined the project and another memo that month indicated it was under way. The main sections of several subsequent progress reports in 1949 were removed by censors before release to the AP.

The broader effort on offensive uses of radiological warfare apparently died by about 1954, at least in part because of the Defense Department's conviction that nuclear weapons were a better bet.

Whether the work migrated to another agency such as the CIA is unclear. The project was given final approval in November 1948 and began the following month, just one year after the CIA's creation in 1947.

It was a turbulent time on the international scene. In August 1949, the Soviet Union successfully tested its first atomic bomb, and two months later Mao Zedong's communists triumphed in China's civil war.

As U.S. scientists developed the atomic bomb during World War II, it was recognized that radioactive agents used or created in the manufacturing process had lethal potential. The government's first public report on the bomb project, published in 1945, noted that radioactive fission products from a uranium-fueled reactor could be extracted and used "like a particularly vicious form of poison gas."

Among the documents released to the AP -- an Army memo dated Dec. 16, 1948, and labeled secret -- described a crash program to develop a variety of military uses for radioactive materials. Work on a "subversive weapon for attack of individuals or small groups" was listed as a secondary priority, to be confined to feasibility studies and experiments.

The top priorities listed were:

-- 1 -- Weapons to contaminate "populated or otherwise critical areas for long periods of time."

-- 3 -- Air and-or surface weapons that would spread contamination across an area to be evacuated, thereby rendering it unusable by enemy forces.

The stated goal was to produce a prototype for the No. 1 and No. 2 priority weapons by Dec. 31, 1950.

The 4th ranked priority was "munitions for attack on individuals" using radioactive agents for which there is "no means of therapy."

"This class of munitions is proposed for use by secret agents or subversive units for lethal attacks against small groups of important individuals, e.g., during meetings of civilian or military leaders," it said.

Assassination of foreign figures by agents of the U.S. government was not explicitly outlawed until President Gerald R. Ford signed an executive order in 1976 in response to revelations that the CIA had plotted in the 1960s to kill Cuban President Fidel Castro, including by poisoning.

The Dec. 16, 1948, memo said a lethal attack against individuals using radiological material should be done in a way that makes it impossible to trace the U.S. government's involvement, a concept known as "plausible deniability" that is central to U.S. covert actions.

"The source of the munition, the fact that an attack has been made, and the kind of attack should not be determinable, if possible," it said. "The munition should be inconspicuous and readily transportable."

Radioactive agents were thought to be ideal for this use, the document said, because of their high toxicity and the fact that the targeted individuals could not smell, taste or otherwise sense the attack.

"It should be possible, for example, to develop a very small munition which could function unnoticeably and which would set up an invisible, yet highly lethal concentration in a room, with the effects noticeable only well after the time of attack," it said.

"The time for lethal effects could, it is believed, be controlled within limits by the amount of radioactive agent dispersed. The toxicities are such that should relatively high concentrations be required for early lethal effects, on a weight basis, even such concentrations may be found practicable."

Tom Bielefeld, a Harvard physicist who has studied radiological weapons issues, said that while he had never heard of this project, its technical aims sounded feasible.

Bielefeld noted that polonium, the radioactive agent used to kill Litvinenko in November 2006, has just the kind of features that would be suitable for the lethal mission described in the Dec. 16 memo.

Barton Bernstein, a Stanford history professor who has done extensive research on the U.S. military's radiological warfare efforts, said he did not believe this aspect had previously come to light.

"This is one of those items that surprises us but should not shock us, because in the Cold War all kinds of ways of killing people, in all kinds of manners -- inhumane, barbaric and even worse -- were periodically contemplated at high levels in the American government in what was seen as a just war against a hated and hateful enemy," Bernstein said.

The project was run by the Army Chemical Corps, commanded by Maj. Gen. Alden H. Waitt, and supervised by a now-defunct agency called the Armed Forces Special Weapons Project. The project's first chief was Maj. Gen. Leslie R. Groves, the Army's head of the Manhattan Project that built the first atomic bombs. The radiological project was approved by Groves' successor, Maj. Gen. Kenneth D. Nichols.

The released documents were in files of the Armed Forces Special Weapons Project held by the National Archives.

Among the officials copied in on the Dec. 16 memo were Herbert Scoville, Jr., then the technical director of the Armed Forces Special Weapons Project and later the CIA's deputy director for research, and Samuel T. Cohen, a physicist with RAND Corp. who had worked on the Manhattan Project.

The initial go-ahead for the Army to pursue its radiological weapons project was given in May 1948, a point in U.S. history, following the successful use of two atomic bombs against Japan to end World War II, when the military was eager to explore the implications of atomic science for the future of warfare.

In a July 1948 memo outlining the program's intent, before specifics had received final approval, a key focus was on long-lasting contamination of large land areas where residents would be told that unless the areas were abandoned they probably would die from radiation within one to 10 years.

"It is thought that this is a new concept of warfare, with results that cannot be predicted," it said.